Bluetooth

Android provides a default Bluetooth stack that supports both Classic Bluetooth
and Bluetooth Low Energy. Using Bluetooth, Android devices can create personal
area networks to send and receive data with nearby Bluetooth devices.

In Android 4.3 and later, the Android Bluetooth stack provides the ability to
implement Bluetooth Low Energy (BLE). To fully leverage the BLE APIs, follow
the Android
Bluetooth HCI Requirements.
Android devices with a qualified chipset can implement either Classic
Bluetooth or both Classic Bluetooth and BLE. BLE is not backwards compatible
with older Bluetooth chipsets.

In Android 8.0, the native Bluetooth stack is fully qualified for Bluetooth 5.
To use available Bluetooth 5 features, the device needs to have a Bluetooth 5
qualified chipset.

Note: The largest change in the native
Bluetooth stack between Android 8.0 and previous versions is the use of
Treble. Vendor implementations in
Android 8.0 must use HIDL instead of libbt-vendor.

Android 8.0 architecture

A Bluetooth application communicates with the Bluetooth process through
Binder. The Bluetooth process uses JNI to communicate with the Bluetooth stack
and provides developers with access to various Bluetooth profiles. This
diagram shows the general structure of the Bluetooth stack:

Figure 1. Android 8.0 Bluetooth architecture

Application framework

At the application framework level is application code,
which uses the
android.bluetooth
APIs to interact with the Bluetooth hardware. Internally, this code calls
the Bluetooth process through the Binder IPC mechanism.

Bluetooth system service

The Bluetooth system service, located in packages/apps/Bluetooth,
is packaged as an Android app and implements the Bluetooth services
and profiles at the Android framework layer. This app calls into the native
Bluetooth stack via JNI.

JNI

The JNI code associated with android.bluetooth is located in
packages/apps/Bluetooth/jni. The JNI code calls into the
Bluetooth stack when certain Bluetooth operations occur, such as when
devices are discovered.

Bluetooth stack

The default Bluetooth stack is provided in AOSP and is located in
system/bt. The stack implements the generic Bluetooth HAL and
customizes it with extensions and configuration changes.

HIDL

HIDL
defines the interface between the Bluetooth stack and the vendor
implementation. To generate the Bluetooth HIDL files, pass the Bluetooth
interface files into the HIDL generation tool. The interface files are located
in hardware/interfaces/bluetooth.

Bluetooth stack development

The Android 8.0 Bluetooth stack is a fully qualified Bluetooth stack. The
qualification listing is on the Bluetooth SIG website under QDID 97584.

The core Bluetooth stack resides in
system/bt.
Development happens in AOSP, and contributions are welcome.

Android 7.x and earlier
architecture

A Bluetooth system service communicates with the Bluetooth stack
through JNI and with applications through Binder IPC. The system service
provides developers with access to various Bluetooth profiles. This
diagram shows the general structure of the Bluetooth stack:

Figure 2. Android 7.x and earlier Bluetooth architecture

Application framework

At the application framework level is application code, which
utilizes the
android.bluetooth
APIs to interact with the Bluetooth hardware. Internally, this code
calls the
Bluetooth process through the Binder IPC mechanism.

Bluetooth system service

The Bluetooth system service, located in
packages/apps/Bluetooth, is packaged as an Android app and
implements the Bluetooth service and profiles at the Android framework layer.
This app calls into the HAL layer via JNI.

JNI

The JNI code associated with
android.bluetooth
is located in packages/apps/Bluetooth/jni. The JNI code calls
into the HAL layer and receives callbacks from the HAL when certain Bluetooth
operations occur, such as when devices are discovered.

HAL

The hardware abstraction layer defines the standard interface that
the
android.bluetooth
APIs and Bluetooth process call into and that you must implement to have
your Bluetooth hardware function correctly. The header file for the Bluetooth
HAL is hardware/libhardware/include/hardware/bluetooth.h.
Additionally, review all of the
hardware/libhardware/include/hardware/bt_*.h files.

Bluetooth stack

The default Bluetooth stack is provided for you and is located in
system/bt. The stack implements the generic Bluetooth HAL
and customizes it with extensions and configuration changes.

Vendor extensions

To add custom extensions and an HCI layer for tracing, you can create a
libbt-vendor module and specify these components.

Implementing the HAL

The Bluetooth HAL is located in
/hardware/libhardware/include/hardware/bluetooth.h.
The bluetooth.h file contains the basic interface for the
Bluetooth stack, and you must implement its functions.

Profile-specific files are located in the same directory. For details, see
the
HAL File Reference.